Negative pressures in surgical drains.

Laboratory and clinical experiments were done to measure the pressure in tube drains. It was found that the fluid in drains connected to floor bags exerted a negative pressure equal to the height of the fluid column in the tube. There was no negative pressure when the drain opened into a urostomy bag at wound level. It is suggested that this negative pressure might tend to maintain a urinary fistula once a leak in the suture line has begun.